Tube control apparatus



H. L. GLICK TUBE CONTROL APPARATUS Sept. 19, 1950 Filed Dec. 17, 1948 INVENTOR Harvey L. Glick.

BY Z.

ATTORNEY Patented Sept. 1 9, 1950 TUBE CONTROL APPARATUS Harvey L. Glick, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 17, 1948, Serial No. 65,946

This invention relates to a control apparatus for electronic tubes and morein particular to a control for equalizing the emission of two temperature limited filaments.

In the application of electronic tubes in various types of control apparatus it is frequently necessary to operate such tubes in pairs. When this is done, it is usually necessary, for proper operation, that the tubes be matched in certain respects.

In the application of X-ray tubes to sheet thickness measurement, the general practice is to provide two tubes, the beam of one of which irradiates the strip the thickness of which is to be measured, and the beam of the other of which irradiates the standard. Thickness measurements are determined by the absorption of the X-ray beam in the material irradiated thereby, and when two tubes are employed having the beam intensities thereof properly matched, comparison of the resulting beams, one of which is the standard, provides an indication of the thickness of the material being inspected.

In applications wherein automatic indications of sheet thickness are to be obtained from the differences in the intensities of the two X-ray beams, and particularly if a null measuring system is employed, it is necessary that the two beams be matched fairly well as to their intensities. Otherwise, errors in the resulting indication may occur.

Accordingly, it is an object of this invention to provide a control for electronic tubes whereby selected characteristics of at least a pair of such tubes are controlled in a predetermined manner.

More specifically, it is an object of this invention to provide a system of the character mentioned in which a control of emission currents of the tubes is obtained.

Still more specifically, it is an object of'this invention to provide a system of the character referred to embodying a pair of X-ray tubes in which emission currents are controlled as a function of the difference of emission currents be tween the tubes.

The foregoing statements are merely illustrative of the various aims and objects of this iii-- vention. Other objects and advantages. will become apparent from a study of the following disclosure when considered in conjunction with the accompanying drawing in which:

Figure 1 is a diagrammatic illustration of an electrical system embodying the principles of this invention, and

7 Claims. (crest-'94) Fig. 2 is a diagrammatic-illustration of a modification of the circuit system of Fig. 1.

' A requirement of an X-ray thickness gauge employing two X-ray tubes is that the target to filament currents, known as the emission cur rents, of the two X-ray tubes shall be equal. These tubes are operated under such conditions of filament temperature and target to filament voltage that the emission. current is dependent only on filament temperature which in turn may be controlled by filament voltage. An example. of a system employing X-ray tubes in this manI-I ner appears in the co-pending application. of the applicant, Serial No. 65,945, filed on'the'same day as this application and entitled. Continuous Strip Tester. With asystem' as briefly noted above, any emissionequalizer must vary the filae ment temperatures until the emission currents are equal. vAs the filament. characteristics change with time, the equalizer must operate continuously,

The energizing circuit arrangement for each of the tubes herein disclosed is a conventional circuit fora self-rectified X-ray tube and each instance embodies a high-voltage transformer giving the required target to filament voltage which may be varied by changing the variable transformerassociated therewith. -Filament temperature and emission currents are adjusted by means of a second transformer feeding a step-down transformer connected with the filament of the tubes. The emission current of the tube is measured by means of a D. C. milliammeter, connected between the secondary windings of the high potential transformer.

Referring specifically to Fig. l, the X-ray tubes therein employed are designated respectively X5 and Xu. The tube Xu, in anormal thickness measuring apparatus, would irradiate' the material or strip being tested, while the beamof the X-ray tube XS irradiates a standardmate rial. Thereafter the beams are compared as generally described hereinbefore to obtain :an indication of the strip thickness. In such an appli- 3 dal waves. The transformer T6 is provided with a suitable tap so that the target to filament voltage of the X-ray tubes mat be set at the desired value. Thus, with one half cycle of alternating current, it will be appreciated that the voltage on windin g I, for example, will be in a direction that the target potential is above the filament potential. As a. consequence, the tube XS will conduct. At this same instant, due to the reversal of the connection of the transformers, the voltage of the primary winding 2 of the transformer T2 will be in such a direction that the potential of the filament voltage of the tube Xu will be above the potential of the target of that tube. As a consequence, the tube Xu will not conduct in that half cycle. In the next half cycle of alternating current this condition is reversed and the tube X is out 01f while the tube Xv. becomes conductin The se'condary'winding system of each of the transformers Ti and T2 includes a pair of windings. For the transformer T2 these windings are designated 3 and 4. One side of the winding 3 is connected to the target of the tube Xu and one side of the winding 4 is connected to the filament of the tube. The remaining terminals 3a and 4a of the secondary windings 3 and 4 are connected across a pair of series connected capacitors CI and C2, the two common terminals of which are connected to ground. The secondary windings 5 and 6 of the transformer TI are connected in a manner similar to the secondary windings 3 and 4 of transformer. T2, one terminal of the windingE being connected to thetarget of the tube X5 and one terminal of the winding 8 being connected to the filament of the tube XS. The remaining terminals 5a and 6a are connected across a pair of series connected gas tubes NEI and NE2, the common terminals of which are grounded and the terminals 5a and 6a are then connected in reversed order across the capacitors CI and C2. The filament voltages for the tubes X5 and Xu are supplied respectively by the transformers T3 and T4, the secondary windings I and 8 of which are connected across the respective filaments of X-ray tubes. Energizing voltage for these filament transformers is provided by means of a transformer T5 having an adjustable tap and this transformer is connected across the source of alternating current.

By reason of the grounding of the common terminals of the capacitors CI and C2, the terminals 3a and 4a of the secondary windings 3 and 4 and the terminals 5a and Ba of the secondary windings 5 and 6 are maintained at ground A. C. potential, but the circuit system provides for the series circuit. Thus, it will be appreciated that the rectified currents of both of the tubes flow through a series circuit and that these currents are employable in charging of the capacitors CI and C2 in one direction or the other, depending upon which of the tubes has the greater emission current. If the emission of one X-ray tube filament is less than that of the other, the current difierence between the two tubes will charge the capacitors CI and C2 to a D. C. potential, the polarity of this D. C. potential depending upon which X-ray tube has the greater emission. This potential appears across the grids GI and G2 of the two vacuum tubes VI and V2, and thus affords a control'of the output of each of these tubes. The cathode circuit of the tubes VI and V2 conventionally includes the capacitor C3 and the resistor RI in parallel, and this circuit is rounded.

The circuit connections for the tubes VI and V2 include a transformer Tl, having a primary winding II, which, as illustrated, is connected across the transformer T5. In view of this connection, adjustments of the tap of transformer T5 produce changes in voltage across the primary winding II. This may be obviated, if necessary, by connecting the primary winding II directly to the source of alternating current. The transformerTl includes a pair of secondary windings I2 and I3, the inner terminals of which are connected together and the outer terminals of which are respectively connected to the grids G3 and G4 of the vacuum tubes VI and V2. With this arrangement, an alternating voltage control is imposed upon the tubes VI and V2, such that the instantaneous polarity of the potential, or phase of the potential, on the grid GI is opposite to that on G2. The tubes VI and V2 amplify the alternating current voltages on their respeccirculation of the rectified currents of the X-ray and through the secondary winding 6 to theouter terminal of the gas-filled tube NE'I, thence to the outer terminal of the capacitor C2 through the milliammeter MA and the secondary winding 3 to the target of the tube X11. From the target of this tube the circuit is traceable to its filament and through the 'secondarywinding 4 to the outer'terminal of the capacitor. CI and the outer terminal of the gas-filled tube NEZ and thence back-to theterm'inal 5a to complete the Sucha circuit may be tracedtive grids CH. and G2, the magnitude of the alter nating current output of VI being controlled by the essentially D. C. voltage on the grid GI and the alternating current output of V2 being controlled by the essentially D. C. voltage on G2. The plate circuits of the tubes VI and V2 include the primary windings I4 and I5 of the transformer T8, the plates PI and P2 being connected to the lower ends of the windings I4 and I5, respectively. Plate voltage is supplied to this plate circuit at the upper ends of both windings from the source designated B+. It will be appreciated that since the phase of the A. C. voltage on GI is opposite to that on G2, the phase of the alternating current through the tube VI and the winding M of T8 will be opposite in phase to the alternating current through the tube V2 and the winding I5 of T8, but these currents will generally be of different magnitude. .It will be further appreciated that the effective current in the windings l4 and I5 will be the algebraic sum of the currents in these windings, and that this effective current will have the phase sense of the larger of the two currents. By means of these currents the tubes VI and V2 control a second set of amplifier tubes :V3 and V4 in one embodiment of my invention. In this embodiment the trans-- former T8 includes a pair of secondary windings l6 and I! having their inner ends connected to- 'gether to ground and their outer ends connected to the respective grids of the tubes V3 and V4. An electrical connection is made from the lower end 2I of the winding ll of T8 to the common connection of the windings I2 and I3 of Tl, thus giving inverse feedback to the tubes VI and V2 which has the well known efiect of reducing arnpiifier distortion. The cathodes of these two tubes are grounded through the resistor R2, and the plates of .the tubes V3 and V4 areconnected across the .primary winding I18 of the-transformer T9, plate voltage designated B+ being applied to a center tap of this primary winding.

The voltage appearing across the primary Winding T9 in magnitude corresponds to the amount of correction required to restore the emission currents of the tubes X5 and Xu to equal levels. The instantaneous phase relation of this voltage with respect to the source of alternating current indicates the sense or direction in-which the correction must be made to achieve equality of emission currents. This controlvoltage is introduced into the filament transformer circuits by means of the secondary windings l9 and 20 of the control transformer T9 which are respectively connected in series with the'primary windings 9 and 100i filament transformers T3 and T4 across the tapped portion of the filament control transformer T5,. Thus, for

example, the voltage of the secondary winding I19 for one condition of correction will add tothe voltage of the winding '9, while the voltage of .the winding 20 for the assumed condition will sub stract from that of the winding Iii. For this assumed condition, the voltage applied to thefilamentof the tube XS will be increased while that supplied to the tube Xu will be decreased. Since the filament temperature is a function of the voltage applied. to the filament, it will be appreciated that the filament having the higher voltage will operate at the higher temperature and as a consequence, its emission will be the greater. Thus, for the assumed condition, the emissionof the tube XS was ,less than that of the tube X11 and the correctionin this instant is of a magnitude and a directionto oppositely vary the emission currents in the direction of zerodifference. In a second embodiment of m invention, the tubes V3 and V4, and the transformer T9 are left out, and the windings l6 and ll of T8 are connected directly .in placeof the windings 20 and IQ of T9. These changes merely change the sensitivity of the system, but do not change the principles of my invention.

The modification of the invention illustrated in Fig. 2 difiers from that of Fig. 1 only in the sense that a single high 'voltagetransformer is provided to energize the tubes X5 and Xu. In this embodiment of the invention the high voltage transformer is designated Till. Its primary windin'g 25 is connected to the source of alternating current and its two secondary windings 26 and 21 are connected across the two X-ray tubes. As before, the common terminals of the windings 26-and 21 are connected acrossthe capacitors Cl and C2 and similarly are connected across the tubes NE! and ,NEZ, the common terminals of the capacitor and the tubes being grounded. The remainder of this circuit system corresponds to that illustrated in Fig. 2 and its and 1-2.1 places the target of the tube =Xs at a higher potential than the filament. Thus tube XS conducts, but since the tube Xu is inverted in this circuit, its filament is above its target in potential and the tube is therefore non-conducting. In the next half cycle of alternating current the voltage across the tubes reverses and the target of the tube Xu is at a. potential higher than :its filament and is thus conducting while the filament of the tube X5 is at a potential :higher than its target and is non-conducting. Thus, the tubes are conducting on alternating half cycles.

The discharge tubes NE] and NEZ are provided as a safety measure in each of'the circuits. In case. of circuit failure, the tubes NE] and :NE2

, break down and become conducting. This preone control voltage circuit while decreasing the illustrative and not interpreted in a limiting sense.

I claim as my invention:

3.. Apparatus for controlling the filament voltage: of a pair of tubes each having an anode and a filament comprising, in combination, circuit means connecting the anode of one tube to the filament of the other tube and the anode of said other tube to the filament of said one tube to provide a series circuit for the emission currents of tubes, circuit means electrically connected with said series circuit for applying energizing voltages to said tubes, capacitor means connected across said series circuit and having a common terminal thereof grounded, a control voltage circuit connected to each filament for energizing the filament of each tube, and circuit means electrically connected across said capacitor means to respond to the voltage across said capacitor means for increasing the voltage of means grounding the common terminals of said capacitors, a control voltage circuit connected to each filament for energizing the filament of each of said tubes, and circuit means electrically connected across said capacitors to respond to the voltage across said capacitors for increasing the voltage of one control voltage circuit while decreasing the voltage of the other control voltage circuit.

3. Apparatus for controlling the filament voltages of a pair of X-ray tubes each having a target and a filament comprising, in combination, circuit means connected with the target and filament of each X-ray tube for applying energizing A. C. voltages to said tubes to effect operation thereof on alternate half cycles of alternating current, circuit means connecting said target and said filament of each X-ray tube in a common series circuit, so that the emission currents of said tubes fiow in said series circuit, a pair of capacitors connected in series across said series circuit, circuit means grounding the common terminals of said pair of capacitors, control circuit means for energizing the filament of each X-ray tube, and circuit means responsive to the voltage across said capacitors for controlling said control circuit means. v

4. Apparatus as set forth in claim 3 in which said control circuit means comprises a pair of transformers each having a primary and a secondary winding, the secondary winding of each of said transformers being connected across the associated one of said filaments,'a control transformer having a primary winding and a pair of secondary windings, circuit means connecting a secondary winding of .the control transformer in series with the primary winding of one of said pair of transformers so that each primary winding of each of the pair of transformers is connected in series with the corresponding secondary winding of the control transformer, circuit means for applying alternating current across-said series connected windings and circuit means connect- :ing said primary Winding of said control transformer to be energized in dependence of the voltage across said capacitors.

5. Apparatus for controlling the filament voltages of a pair of tubes each having an anode and a filament comprising, in combination, a pair of transformers each having a primary Winding and at least one secondary winding, circuit means including the secondary winding of each transformer connecting the anodes and filaments of said tubes in a series loop, circuit means connecting the primary windings of said transformers together and providing for the common connection of said transformers to a source of alternating current, the phase relation of the secondary winding voltages in said series loop energizing one tube while blocking the other and energizing said other tube while blocking said one tube on successive half cycles of alternating 'current, impedance means connected across said :series loop to respond to the difference of emis- :sion currents of said tubes and produce an electrical quantity in dependence thereof, an ener- 'gizing circuit for each filament connected to the filament of each of said tubes,and circuit :means for applying said electrical quantity to teach energizing circuit.

6. Apparatus for controlling the filament voltages of a pair of tubes each having an anode and ;a filament comprising, in combination, a pair of transformers each having a primary winding and :at least one secondary winding, circuit means including the secondary winding of each trans former connecting the anodes and filaments of said tubes in a series loop, circuit means connecting the primary windings of said transformers together and providing for the common connection of said transformers to a source of alternating current, the phase relation of the secondary winding voltages in said series loop energizing one tube While blocking the other and energizing said other tube while blocking said one tube on successive half cycles of alternating cura filament comprising, in combination, circuit nating current, circuit-means electrically connected with said series loop to respond to the difference of emission currents of said tubes and produce an electrical quantity in dependence thereof, an energizing circuit connected with each filament for applying an alternating current voltage to the corresponding filament, and circuit means responsive to said electrical quantity and electrically connected with each energizing cir- ,cuit for applying said electrical quantity in aiding relation in one energizing circuit and in a subtractive relation in the other energizing circuit.

HARVEY L. GLICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,625,328 Mutscheller Apr. 19, 1927 1,921,499 Bishop Aug. 8, 1933 1,924,462 Scofield Aug. 29, 1933 2,023,453 Von Wedel lee. 10, 1935 2,032,894 Simon Mar. 3, 1936 2,319,378 1943' Weisglass s l May 18, 

